1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to an image forming apparatus including a developer driving device that does not pass on the overload of a developing roller onto a photosensitive drum by separately actuating the photosensitive drum and the developing roller.
2. Description of the Related Art
Generally, an image forming apparatus forms an electrostatic latent image on a photosensitive medium such as a photosensitive drum, develops the electrostatic latent image into an image with predetermined colors, and transfers, fuses and fixes the image onto a print paper, thereby producing a desired image.
Such an image forming apparatus has a developer, which can develop the electrostatic latent image into an image with predetermined colors, detachably installed in a main body frame. The developer accommodates a developing agent within a housing, and includes a photosensitive drum on which the electrostatic latent image is formed by an exposing unit, a developing roller that supplies the developing agent to the photosensitive drum and develops the electrostatic latent image, and a supplying roller that supplies the developing agent to the developing roller.
FIG. 1 is a perspective view of an example of a conventional developer driving device, FIG. 2 is a cross-sectional view of the developer driving device of FIG. 1, and FIG. 3 is a cross-sectional view of another example of a conventional developer driving device.
Referring to FIGS. 1 and 2, a housing 33 (see FIG. 2) covers a photosensitive drum 30 and a developing roller 40, and a photosensitive drum driving gear 31 is installed on one side of the photosensitive drum 30. The photosensitive drum 30 is rotatably supported by a photosensitive drum axis 32 that passes through the photosensitive drum driving gear 31. A developing roller axis 42 rotatably supports the developing roller 40, which is located adjacent to the photosensitive drum and develops the electrostatic latent image by supplying toner to the photosensitive drum 30. A developing roller driving gear 41 is installed on one end of the developing roller axis 42 to mesh with the photosensitive drum driving gear 31 and rotate. A portion of the photosensitive drum 30 is exposed out of the housing 33 and contacts a transfer roller (not shown). The photosensitive drum 30 transfers the toner image onto a print paper (not shown).
A portion of a driving gear 20 exists outside the main body frame 21, and is supported rotatably. The driving gear 20 rotates in connection to a main motor 10, and rotates the photosensitive drum driving gear 31.
Therefore, the photosensitive drum 30 rotates with the photosensitive drum driving gear 31, which is meshed with the driving gear 20, which is driving by the main motor 10. Simultaneously, the developing roller 40 rotates with the developing roller driving gear 41, which is meshed with the photosensitive drum driving gear 31.
However, a jitter, which results in image irregularity in a printed image, can easily develop since an overload to the developing roller 40 affects the photosensitive drum 30, resulting in irregular rotation, due to the meshing of the photosensitive drum driving gear 31 and the developing roller driving gear 41. In addition, the photosensitive drum 30 transports through rotation, a print paper even when an image is not developed. In this case, the developing roller 40 continues to be driven by the developing roller driving gear 41, which is meshed with the photosensitive drum driving gear 31, thereby applying stress to the toner and lowering print quality.
Referring to FIG. 3, in order to prevent the problems of the conventional developer driving device of FIGS. 1 and 2, a coupler 51, which connects a photosensitive drum driving gear 31 and a developing roller 40, is installed in a main body frame 21, and is able to slide in the direction depicted by the arrows in FIG. 3. Therefore, the coupler 51 connects the photosensitive drum driving gear 31 and the developing roller 40, and drives the developing roller 40 only when performing a developing operation.
When mounting a developer on a main body frame, however, a door and a link structure are necessary to prevent contact with the coupler 51. Thus, there are limits to minimizing the size of the main body frame and the production price.